A hybrid powertrain system typically includes torque-generative devices which provide motive torque to a transmission device to control torque and speed output to a driveline. The torque-generative devices typically comprise an internal combustion engine and electric machines. An exemplary hybrid powertrain includes a two-mode, compound-split, electro-mechanical transmission operative to receive torque input from the torque-generative devices. Management of the torque inputs to achieve an output includes selective actuation of torque-transfer devices, or clutches, of the transmission. Actuation of each clutch is effected via selectively applied hydraulic pressure from a hydraulic circuit. Pressurized fluid through the hydraulic circuit is typically supplied from a hydraulic pump that is driven off of an input shaft from the internal combustion engine.
A second, electrically-driven hydraulic pump can be selectively operated to supply pressurized fluid to the hydraulic circuit as required. By way of example, a vehicle employing a hybrid powertrain reduces fuel consumption and improves fuel economy by selectively shutting off the internal combustion engine under specific operating conditions, e.g. when the vehicle is stopped at a stoplight, or coasting. Under such conditions, the engine-driven hydraulic pump is inoperative and unable to maintain fluidic pressure in the hydraulic circuit. An applied torque-transfer clutch may deactivate due to leak down of hydraulic pressure. Engineers have addressed the issue of leak down of hydraulic pressure during engine shutoff events by mechanizing systems with the aforementioned electrically-driven auxiliary hydraulic pump to supply hydraulic pressure to the torque-transfer clutches during such events.
A fault occurring in a system employing an electrically-driven auxiliary hydraulic pump leads to the hybrid system not operating as intended, resulting in customer dissatisfaction. Furthermore, federal and state regulations impose requirements to monitor operation of such pumps, including diagnosing presence of a fault and informing a vehicle operator of the presence of the fault, under specifically regulated conditions. System elements requiring monitoring can include sensing devices, actuators, electric motors, and electrical circuits. Monitoring conditions can include presence of open or short circuits, out-of-range/rationality checking, and proper functional response to inputs. Therefore, there is a need for a control system to monitor operation of an electrically-driven auxiliary hydraulic pump and system.